Explicit Interface Implementation demanded, but only one interface in use?

Question

Why does the following code have to have 'CalcUsable' defined using Explicit Interface Implementation syntax? (see last line of code) If I use non-explicit syntax, (ie. public decimal CalcUsable) I get an "inconsistent accessibility" error, specifically:

"Parameter type ...List (IVoucher) is less accessible than method CalcUsable(...)"

interface IVoucher
{
    string Serial { get; }
    decimal FaceValue { get; }
    string DiscountType { get; }
    string ApplyMsg { get; }
    string RejectMsg { get; }
    decimal CalcUsable(List<Product> products, List<IVoucher> vouchers);
}

// 'GiftVoucher' models the simple voucher which has no use restrictions.
//
public class GiftVoucher : IVoucher
{
    public string Serial { get; private set; }
    public decimal FaceValue { get; private set; }
    public string DiscountType { get; private set; }
    public string ApplyMsg { get; private set; }
    public string RejectMsg { get; private set; }

    public GiftVoucher(string serial, decimal faceValue)
    {
        Serial = serial;
        FaceValue = faceValue;
        ApplyMsg = string.Empty;
        RejectMsg = string.Empty;
        DiscountType = "Gift";
    }

    // 'CalcUsable' provides the voucher applicability logic.  
    //
    decimal IVoucher.CalcUsable(List<Product> products, List<IVoucher> vouchers)
    {
         blar, blar, blar...

Try making your interface public – Jacob Lambert Dec 13 '14 at 19:49 — Jacob Lambert, Dec 13 '14 at 19:49

score 3 · Accepted Answer · answered Dec 13 '14 at 19:55

3

The class GiftVoucher is public whereas the interface IVoucher is not. As such, CalcUsable could not be called from anywhere where IVoucher is not available as the method takes a List of a type that isn't accessible.

As JRLambert suggested, making the interface public should solve this.

answered Dec 13 '14 at 19:55

Adam H

1,523
11
21

I thought the default accessibility for Interface was public? If not, what is it? – CodeCabbie Dec 13 '14 at 20:01
2

Default access modifier for the type in C# is `internal` (I'm not sure about nested types). – Dennis Dec 13 '14 at 20:06
It might well be better to remove the `public` modifier from the class (so as to make it `internal` just like the interface). – Jeppe Stig Nielsen Jan 26 '15 at 17:26
@CodeCabbie The default accessibility for a **member** (e.g. method) of an interface is `public`. It is the only allowed access level, so you are not even allowed to specify it. Example: Your declaration `decimal CalcUsable(List products, List vouchers);` inside the interface is `public`. The default access level of the `interface` itself depends on what the interface is a direct member of. If it is a direct member of a `namespace`, then the default accessibility of namespaces apply, which is `internal`. But if the interface is a member of a class or a struct, `private`. – Jeppe Stig Nielsen Jan 26 '15 at 17:32

Explicit Interface Implementation demanded, but only one interface in use?

1 Answers1